The invention relates to an internal mixer having a mixer housing in which are disposed mixing means and which has a charging opening that can be closed off by a press or floating weight, with a charging hopper being placed on the charging opening and being provided with at least one closeable filling opening, with the floating weight being guided in an upwardly and downwardly slidable manner in the charging hopper, and being movable between various positions in the hopper via a hydraulic actuating mechanism that includes pistons, piston rods, and piston chambers, with a hydraulic control mechanism being associated with the actuating mechanism.
Such internal mixers are used for procedures in the preparation of plastic materials, especially rubber, with the plastic materials and the additives being successively introduced into the internal mixers, where they are thoroughly mixed, kneaded or masticated, and finally discharged. During these procedures, considerable forces act upon the floating weight; however, these forces must not lead to swinging or tilting of the hydraulic actuating mechanism.
Pursuant to a known internal mixer of the above identified type (DE 34 26 442 C1 in the name of Manfred Stahr and dated Dec. 5, 1985), the floating weight is secured to the movable cylinder housing, while the piston and the piston rods are secured via spherical mountings to a construction that is secured to the housing and that contains a cross member and a tie rod. This construction projects upwardly to a relatively great extent in conformity to the maximum extension length of the hydraulic actuating mechanisms; this can have an adverse impact upon the transverse transport of materials in the plant where the internal mixer is located. If the internal mixer is to have an overall height that corresponds to the operating height of the crane above the floor, it is no longer possible to move the crane over the internal mixer. While pneumatioally driven internal mixers have a certain buffering resilience of the floating weight during the mixing operation--and for this reason have to accept the drawback of greater energy losses due to the pneumatic operation--hydraulically driven internal mixers of the previously known type are to a certain extent stiff or inflexible; in other words, the floating weight can hardly yield at all when impacts are encountered during the mixing operation.
It is an object of the present invention to provide an internal mixer that has a hydraulic actuating mechanism and that has a relatively compact construction, whereby however the hydraulic guidance of the piston and its piston rod should remain free from surrounding influences in the charging hopper. Furthermore, the floating weight, despite its hydraulic drive, should be floatingly held in the mixing operation position, such as upon a buffer.